Rate of lacrimal excretion of ophthalmic vehicles

Prednisolone and dexamethasone are systemically absorbed after topical application of ophthalmic suspensions in healthy dogs

OBJECTIVE

To quantify plasma concentrations of prednisolone and dexamethasone (peripheral and jugular) and cortisol following topical ophthalmic application of 1% prednisolone acetate and 0.1% dexamethasone to healthy adult dogs.

ANIMALS

12 purpose-bred Beagles.

PROCEDURES

Dogs received 1 drop of 1% prednisolone acetate (n = 6) or neomycin polymyxin B dexamethasone (ie, 0.1% dexamethasone; 6) ophthalmic suspension in both eyes every 6 hours for 14 days. Blood samples (peripheral and jugular) were collected on days 0, 1, 7, and 14 and analyzed for plasma prednisolone and dexamethasone concentrations. Plasma cortisol concentrations were measured at the beginning of the study and following topical drug administration.

RESULTS

Both drugs demonstrated systemic absorption. Prednisolone was detected on days 1, 7, and 14 (median plasma concentration, 24.80 ng/mL; range, 6.20 to 74.00 ng/mL), and dexamethasone was detected on days 1, 7, and 14 (2.30 ng/mL; 0 to 17.70 ng/mL). Neither prednisolone nor dexamethasone were detected in plasma samples on day 0 (baseline). Sampling from the jugular vein resulted in higher plasma drug concentrations than from a peripheral vein when samples from each day were combined. Plasma cortisol concentrations were significantly lower than baseline following 14 days of treatment with topical prednisolone acetate and dexamethasone.

CLINICAL RELEVANCE

Prednisolone and dexamethasone are detected in the plasma of healthy dogs following topical ophthalmic administration 4 times/d with prednisolone concentrations being close to a physiologic dose of orally administered prednisolone. Additional research is needed to evaluate the systemic absorption of these medications in dogs with ocular inflammation.

In vitro and in vivo effects of a lubricant in a contact lens solution

PURPOSE

Physical properties and tear film function were investigated for a multipurpose contact lens solution containing the ocular lubricant hydroxypropyl methylcellulose (HPMC).

METHODS

In the laboratory, wetting properties of multipurpose solutions with and without HPMC, and binding of HPMC to hydrogel lenses in vitro following an overnight soak, were measured. Tear physiology was evaluated in 35 hydrogel contact lens wearers using multipurpose solutions with and without HPMC. Pre-lens tear evaporation rate (TER), tear thinning time (TTT) and tear film structure (TFS) were recorded, and subjective responses were obtained.

RESULTS

Laboratory measurements indicated improved wetting with the HPMC-containing solution, and continued release of HPMC from lenses after an overnight soak in the solution. Pre-lens TTT was longer (p < 0.001) and pre-lens TFS was improved (p = 0.034) with use of the HPMC-containing solution. Pre-lens TER and subjective comparisons did not demonstrate significant differences.

CONCLUSIONS

In vitro and in vivo results are consistent with HPMC producing a thicker, longer-lasting layer of fluid on the hydrogel lens, leading to improvements in tear function in contact lens wearers.